1. Field of Invention
The invention relates to a power supplying apparatus for use in an image forming apparatus that supplies power to an electrical load in an image forming apparatus and, more specifically, to a power supplying apparatus capable of preventing occurrence of a power surge when the electrical load is powered on.
2. Description of Related Art
As a typical electrical load in an image forming apparatus, a fixation device for use in, for example, copiers, laser printers and the like, is known which heats and fixes toner transferred from a photosensitive drum, or the like, to a recording medium, such as a copy paper sheet, or the like. In such a fixation device, a heater employing a halogen lamp, or the like, has been considered for use as a fixation-heating device for fixing toner by heating. It has also been considered that the surface temperature, or the like, of a heating roller having a built-in heating lamp is detected by a thermister (thermal resistor), or the like, and the power supplied to the lamp is controlled by using a triac (triode AC switch), or the like, so that the roller surface temperature, or the like, becomes equal to a desired temperature.
FIG. 7 is a timing chart illustrating an example of the aforementioned control. In the control illustrated in FIG. 7, a lamp-vicinity temperature (A) is detected by a thermister, or the like, and a heating lamp is switched on and off (B) so that the lamp-vicinity temperature (A) changes between a minimum value TA and a maximum value TB. That is, if the temperature decreases to TA, the lamp is switched on. The on-state of the lamp is continued until the temperature increases to TB. When the temperature reaches TB, the lamp is switched off. The off-state of the lamp is continued until the temperature decreases to TA. When the temperature decreases to TA, the lamp is switched on again. This control is repeated.
During this control, however, immediately after the lamp is switched on, that is, immediately after power is supplied to the lamp, a large or surge current (normally termed a power surge) flows through the lamp as indicated in FIG. 7. In a case where a copier, or the like, and lighting fixtures, and the like, are connected to a common power source as in an office, the power voltage of the lighting fixtures decreases every time the power surge flows through the copier, or the like. If a power surge occurs, for example, at a frequency of about 8.8 Hz, there occurs an undesired flickering of the lighting fixtures. Considering the recent increase of the use of large-power heating lamps of about 10 kW as fixation-heating devices, prevention of flickering caused by the power surge is desired. In addition to the flickering, the voltage fall caused by the power surge can possibly have other adverse effects on various appliances.